1. Field of the Invention
The invention relates generally to water drainage systems for buildings, and more particularly to a secondary water drainage system for buildings which are constructed using pre-manufactured exterior panels or cladding, such as Architectural Precast Concrete (xe2x80x9cAPCxe2x80x9d), Glass Fiber Reinforced Concrete (xe2x80x9cGFRCxe2x80x9d), Composite Architectural Precast (xe2x80x9cCAPxe2x80x9d), or Natural Stone on a Truss Frame system (xe2x80x9cNSTFxe2x80x9d).
2. Description of the Prior Art
Modern mid to high rise building are predominately constructed from a structural steel or cast-in-place concrete framework, upon which all other building elements are mounted and supported. For example, walls, floors, and electrical, plumbing, and HVAC systems are all integrated with and attached to the steel or concrete supporting structure. The exterior of the supporting structure is typically covered with the above-referenced pre-manufactured panels or cladding. Other common exterior coverings include glass, curtain wall systems, metal panels, stucco, Exterior Insulation Finish Systems (xe2x80x9cEIFSxe2x80x9d), plaster, and brick. All such exterior coverings must be carefully designed, constructed, and installed to comply with existing building specifications respecting air and water infiltration.
Exterior panels and cladding, being of a discrete size, have vertical and horizontal joints between adjacent panels. These joints must be sealed against air and water infiltration. For that purpose, high performance elastomeric sealants have been developed. The term elastomeric refers to a material""s ability to compress or elongate when a stress is applied, and return to its original state when the stress is removed. These elastomeric properties are necessary to accommodate joint movements resulting from thermal expansion and contraction, inter-story building drift owing to wind forces or seismic movement, or elastic frame shortening and creep. State of the art elastomeric sealants exhibit high tolerance to joint movement, being able to accommodate movements on the order of plus or minus 25% of the joint""s transverse dimension.
Silicone-based elastomeric sealants are commonly used to protect exterior panel or cladding joints from water intrusion. The manner of installation of the sealant is straightforward, but certain precautions must observed. The sealant is typically installed over a backer rod, made of polyurethane or polyethylene foam. The backer rod is initially installed along the full extent of the joint between the panels. Then, the silicone sealant is applied into the joint, against the side edges of the panels and the backer rod. The backer rod supports the sealant until it has fully sealed, and also ensures that a proper joint configuration is formed which will allow the sealant to expand and contract as required. The combination of the exterior cladding with the silicone sealant in the joints, forms the primary waterproofing barrier for the building.
The quality of this primary waterproofing barrier is highly dependent upon the skilled workmanship of the installer. For example, the installer must properly detail the bond line of the joint, by cleaning the opposing side edges of the adjacent panels so the sealant will properly adhere to the panel. The location and depth of the backer rod must be correct, to ensure that the sealant joint will have sufficient flexibility and resiliency to withstand expansion, contraction, and flexure forces. The integrity of the waterproofing barrier is also contingent upon the consistency, quality, and selection of the particular sealant used. The sealant which is most appropriate in an architectural precast concrete panel-to-panel joint, for example, may not be the proper sealant for an architectural precast concrete panel to an aluminum window mullion joint.
A failure of the waterproofing barrier can also occur when the exterior panels themselves are cracked or damaged, allowing water to pass directly through the panels. Failures in the barrier may occur at the interface between the glass and the curtain wall systems. The passage of time, including deterioration of materials, extreme temperatures, exposure to the sun, and seismic events, may all contribute to a joint failure or some other compromise in the integrity of the waterproofing barrier. Unfortunately, failure or compromise of the primary waterproofing barrier can occur with little or no warning, causing water or air intrusion.
When water leaks do occur, the damage caused to the building can further be amplified by percolation. Percolation arises when sustained high winds, or a positive external pressure caused by the operation of the building""s HVAC, can literally vacuum water through the damaged sealant joints or cracked cladding. The water then bubbles or percolates into the building, causing more damage.
Another source of concern derives from condensation on the rear or backside of the panels. Sealants in the joints protect the interior region of the panels from leaks, but do nothing to protect against condensation. Under certain atmospheric conditions, water can condense on the backside of the panels even where no joint leak or panel cracking has occurred. The occurrence and extent of such condensation varies with the geographical location of the building, the type or lack of a vapor barrier, and the amount and temperature of the air infiltration into the building. When these factors favor the formation of condensation, the airspace between the panels and the supporting structure reaches 100% relative humidity. As the panels cool, condensation forms on their backsides.
Buildings also contain varying amounts of incidental moisture, resulting from small amounts of moisture which transmigrate through the panels or cladding. This occurs as a consequence of undetectable imperfections in material and workmanship. Most of the time, the leaks or condensation which produce this incidental moisture are so insignificant that the incidental moisture is absorbed by the substrate of the panels, and dries prior to any damage occurring. However, if the incidental moisture content exceeds the threshold saturation capacity of the substrate, the excess moisture may lead to interior damage to the building and promote mold growth.
The prior art teaches a number of different backup or secondary drainage systems to remove water or condensation from the rear side of exterior panels or cladding for modern buildings. For example, in Rizza, U.S. Pat. No. 5,289,664, a back drainage system for exterior panels is disclosed. An open gutter extends along the back wall of a panel, and includes a weep tube at one end extending toward the front wall of the panel. A piece of reticulated foam within the weep tube is claimed to allow water to flow out, while preventing moisture backup through the tube and wind noise. In U.S. Pat. No. 4,924,647, granted to Drucker, an exterior wall panel drainage system is shown. Gutters collect water from the rear wall, and drain tubes and weep holes drain the collected condensation to the outside of the panel wall. U.S. Pat. No. 6,216,406, issued to Smith, shows a mounting and draining system for prefabricated building panels. A drain tube extends between an interior gutter and the exterior of the panel. U.S. Pat. No. 5,048,254, granted to Merlau, shows a tapered base plate for collecting water trapped behind the building panel. The water in channeled through drainage holes into weep holes, and thereafter passes outside the building panel.
It is evident from the foregoing prior art that the industry recognizes the problems associated with rear panel condensation and water intrusion resulting from a failure of the primary waterproofing barrier. However, there is considerable room for improvement in the secondary drainage systems developed thus far. For example, percolation back through the drainage lines or weep holes of the prior art drainage systems, is a persistent problem. Prior art systems lack physical and installation flexibility, making them difficult to adapt to a variety of different panel and cladding designs. Power tools are required for the on-site installation of most prior art drainage systems. The known prior art drainage systems have no protection against debris clogging, either during the construction phase of the building or after construction is complete.
The secondary moisture drainage system of the present invention includes one or more elongated collection channels, adhesively or mechanically affixed to the rear wall of a building panel. To encourage positive drainage, the collection channels are maintained in inclined relation, extending from an upper end to a lower drain end. The channels are manufactured from flame retardant, elastomeric silicone, sufficiently flexible to follow the undulations and imperfections in the panels. Each collection channel includes opposing vertical side walls, a bottom floor spanning the side walls, and a perforated top cover. The top cover is effective to keep potentially clogging debris out of the channel. The perforations are preferably oval in configuration, to inhibit capillary action which would otherwise slow drainage through the top cover.
The lower end of each collection channel is fitted with an end cap. The end cap is constructed similarly to the collection channel, but includes a closed wall at one end, and a drain aperture and a drain spout passing water through its bottom floor. The end cap is located adjacent a vertical joint, such as would exist between two panels.
A water receptacle box is provided in each such panel joint. The upper rear portion of the receptacle box is provided with one or more inlet fittings. A drain tube interconnects the drain spout extending from the end cap with an inlet fitting, so that any moisture entering the collection channel will be directed into the receptacle box. The receptacle box is also preferably provided with an open top, to collect water or condensation draining downwardly through the panel joint.
The lower front portion of the receptacle box has a discharge fitting, provided with a one-way discharge valve. A backer rod extends through the full extent of the panel joint, generally above and below the receptacle box. The silicone sealant is injected into the joint, filling the joint between the panels while being supported both by the backer rod and by the front wall of the receptacle box. The one-way discharge valve extends forwardly, completely through the exposed side of the sealant, so that any moisture passing therethrough will be discharged outside upon the front wall of the panel. The one-way valve allows water to discharge to the exterior of the building but prevents percolation into the secondary drainage system and the interior walls of the panels.
A joint gutter may be placed into intermediate panel joints, not provided with a water receptacle box. The joint gutter includes an open top for collection of moisture dripping downwardly through the panel joint. One embodiment of the joint gutter, adapted for panel joints of larger dimensions, has vertical walls, a floor, and a discharge spout centered over the collection channel. Another embodiment of the joint gutter, adapted for more narrow panel joints, is shaped like a curved trough. Since it is made from a resilient material, it is installed by simply squeezing the gutter and inserting it into the joint. Upon release, with its lower discharge end centered over the collection channel. The joint gutter is ready to be silicone sealed into place. Both embodiments of the joint gutter collect excess moisture within the joint, and direct it into the collection channel for eventual discharge outside the building.
It is an object, therefore, of the present invention to provide a secondary drainage system, for buildings employing pre-manufactured panels, which could be field or plant installed, without the use of power tools and with minimal impact on current operations of panel manufacturers.
It is also an object of the present invention to provide such a secondary drainage system manufactured from materials which are non-combustible, compatible with exterior silicone sealants, and non-conducive to mold growth.
It is a further object herein to provide a secondary drainage system which exhibits elastomeric properties to accommodate panel irregularities and joint movements, and which provides water drainage protection for both horizontal and vertical joints between panels.
It is yet another object herein to provide a secondary drainage system which is easy to keep clean and free from construction debris during installation, and provides further safeguards to maintain such performance during the extent of its useful lifetime.
These and other objects of the present invention will be disclosed further in the drawings and in the detailed description of the preferred embodiment, to follow.